The present invention relates to video monitors and, more particularly, to a method and apparatus for eliminating magnetic field interaction between closely positioned video monitors.
There are many instances in which it is desireable to have more than one video monitor in close physical proximity to another. In medical equipment, such as x-ray equipment, it has also become popular to utilize multiple monitors. Typically, one monitor will be an image display monitor and another will be an alpha-numeric (A/N) display monitor. Both types of monitors use standard cathode ray tube (CRT) displays and have essentially identical electron beam control systems using magnetic fields generated by electromagnets or yokes mounted about a neck of the CRT. As will be appreciated, when any two monitors are closely positioned, the magnetic field generated in one monitor may adversely effect the display on an adjacent monitor. This "cross-talk" effect is most noticeable when vertical retrace in one monitor occurs at a different time than a vertical retrace in another and generally appears as a horizontal distortion on one or both of the video displays.
The prior art has attempted to minimize the effect of magnetic interaction by providing magnetic shielding around the necks of CRT's in monitors designed to operate adjacent other monitors. Such shielding increases the cost of a monitor. Other attempts to alleviate the problem have involved the use of higher quality, and more costly, electromagnets and associated drive circuitry to generate a more controlled or tightly defined and shaped magnetic field.
Although the interaction between monitors may occur when driven by identical but unsynchronized video signals, the interaction is more exacerbated when one monitor operates at a different scan rate or frame rate than another. In the medical example above, the x-ray image display data is typically provided as standard 525 line video date; however, the A/N display data is typically provided in a 263 lines per frame, non interlaced video signal format. In displaying these different video formats on adjacent monitors, the vertical retrace in the A/N monitor typically disturbs the video image quality as displayed on the image monitor.
It is an object of the present invention to provide a method and apparatus for eliminating electromagnetic interference between closely positioned video monitors when driven by different video formats.
It is a further object of the present invention to provide a method and apparatus for eliminating electromagnetic interference between closely coupled video monitors without the use of magnetic shielding.